Electric Field and Electric Field Lines

Correct answer: A. Force per unit positive test charge

Explanation: Electric field intensity at a point is defined as the force experienced by a unit positive test charge placed at that point, so E = F/q. The test charge is considered sufficiently small so that it does not appreciably disturb the original field. Therefore option A is correct. Mass, distance per unit time, and temperature describe other physical quantities and cannot define electric field intensity.

Correct answer: B. Vector

Explanation: Electric field is a vector quantity because it has both magnitude and direction at every point. Its direction is defined as the direction of force on a small positive test charge, while its magnitude is force per unit charge, E = F/q. Thus option B is correct. A scalar has magnitude only, and the other choices do not correctly classify a physical field.

Correct answer: A. Stronger field

Explanation: The density or closeness of electric field lines represents the relative magnitude of the electric field. Where the lines are packed more closely, a test charge would experience a larger force per unit charge, so the field is stronger. Hence option A is correct. Widely spaced lines indicate a weaker field; line density does not specify charge colour or merely the size of an object.

Correct answer: B. Weaker

Explanation: In a field-line diagram, the spacing of lines gives a qualitative indication of field magnitude. Lines that are far apart represent fewer lines per unit area and therefore a weaker electric field at that location. Option B is correct. Close spacing would indicate a stronger field, whereas widely separated lines do not necessarily mean the field is zero or infinite.

Correct answer: A. Because field cannot have two directions at one point

Explanation: The tangent to an electric field line gives the direction of the electric field at that point. If two field lines crossed, their tangents would assign two different field directions to the same point, which is impossible for a uniquely defined electric field. Therefore option A is correct. Charges need not be stationary, lines need not be circular, and the field is vector, not scalar.

Correct answer: A. Straight and parallel

Explanation: A uniform electric field has the same magnitude and the same direction at every point in the region. Field lines representing such a field are therefore straight, parallel, and equally spaced. Option A is correct. Curved lines indicate changing direction, intersecting lines would imply two directions at one point, and electric field lines generally begin on positive charge and end on negative charge rather than forming closed circles.

Correct answer: A. Radially outward

Explanation: By convention, the direction of an electric field is the force direction on a positive test charge. A positive source charge repels that test charge, so the field direction is away from the charge in every radial direction. Thus option A is correct. Inward radial lines belong to a negative point charge, while parallel or closed circular lines do not describe an isolated point charge.

Correct answer: B. Radially inward

Explanation: Electric field direction is defined by the force on a positive test charge. A negative point charge attracts such a test charge, so the field vectors and field lines point radially inward toward the charge. Therefore option B is correct. Outward radial lines represent a positive point charge; the negative charge still has field lines, so option D is also incorrect.

Correct answer: A. Direction of field at that point

Explanation: An electric field line is drawn so that its tangent at any point gives the instantaneous direction of the electric field there. Equivalently, it gives the direction in which a positive test charge would be pushed. Hence option A is correct. The tangent does not measure mass, temperature, or the visual thickness of the line; line spacing, rather than thickness, conveys relative field strength.

Correct answer: A. Newton per coulomb

Explanation: Electric field intensity is defined by E = F/q, where F is force in newtons and q is charge in coulombs. Dividing the units gives newton per coulomb, written N/C, so option A is correct. Electric field can also be expressed as volt per metre, V/m, which is equivalent to N/C. The reciprocal unit and product units in the other options do not match the definition.

Correct answer: A. Positive charge

Explanation: The governing concept is the definition of electric-field direction: it is the direction of force on a small positive test charge. A positive source charge repels that test charge, so field lines are drawn outward and considered to start from positive charge. They generally terminate on negative charge or at infinity. Neutrons and uncharged objects do not determine the usual starting convention. Therefore, option A is correct.

Correct answer: B. Negative charge

Explanation: Electric-field lines are a representation of the force direction on a positive test charge. A negative source charge attracts a positive test charge, so the field direction points toward the negative charge. Consequently, field lines are conventionally drawn ending on negative charges; they may also extend to infinity if no opposite charge is present. Light and sound are not electric charges. Therefore, option B is correct.

Correct answer: A. Magnitude of charge

Explanation: Field lines are imaginary graphical tools, not physical objects, and their number is chosen to indicate the relative strength of an electric field. A larger magnitude of charge produces a stronger field, so diagrams conventionally show it with more lines. The exact number is not a measured fixed quantity, but the relative density or number represents charge magnitude. Colour, room size, and sound do not determine it. Option A is correct.

Correct answer: A. Zero

Explanation: The governing relation is F = qE, where F is electric force, q is the test charge, and E is the electric field. At the stated point, E = 0, so for any finite positive test charge, F = q × 0 = 0. Thus the charge experiences no electric force there. The force is not necessarily large, downward, or directionally fixed. Therefore, option A is correct.

Correct answer: A. In the direction of the electric field

Explanation: By definition, the electric field vector at a point is the force per unit positive test charge, expressed as E = F/q. Since the test charge is positive, q > 0, rearranging gives F = qE, so the force vector has the same direction as E. A negative charge would reverse the direction, but that is not the situation here. Hence option A is correct.

Correct answer: B. Opposite to the field

Explanation: The force on a charge in an electric field is given by F = qE. For a negative test charge, q is negative, so multiplication by q reverses the direction of the force relative to the electric-field vector. Therefore, the force acts opposite to the field direction, with magnitude |F| = |q|E. It is not always upward or zero. Thus option B is correct.

Correct answer: A. Imaginary lines used to represent the field

Explanation: Electric field lines are conceptual or imaginary lines used to visualize an otherwise invisible electric field. At any point, the tangent to a line gives the field direction, while greater line density is conventionally associated with greater field strength. They are not material wires, light rays, or sound waves and cannot be physically collected as objects. Therefore, option A is correct.

Correct answer: A. Small positive test charge

Explanation: Electric-field direction is defined as the direction of force that would act on a small positive test charge placed at the point. The test charge must be sufficiently small so that its own field does not significantly disturb the source-charge arrangement. A large negative charge would experience the opposite force direction, while a neutron or massless particle is not the defining reference. Hence option A is correct.

Correct answer: A. Uniform electric field

Explanation: The spacing of field lines represents relative field magnitude, and their orientation represents direction. Equal spacing means the magnitude is the same from place to place, while parallel lines mean the direction is unchanged. Together these features describe a uniform electric field. A non-uniform field would show changing spacing, changing direction, or both. The other choices are not valid descriptions of this electric-field diagram. Option A is correct.

Correct answer: B. With changing spacing or direction

Explanation: A non-uniform electric field has a magnitude, direction, or both that vary from one position to another. In a field-line diagram, changing magnitude is represented by changing spacing, and changing direction is represented by curvature or changing orientation. Thus the lines may become closer, farther apart, or curved. They can still be drawn, and they are not necessarily horizontal. Therefore, option B is correct.

Correct answer: A. Direction of electric field

Explanation: The arrow on an electric field line represents the direction of the electric field at that point. By definition, this is the direction of force that a small positive test charge would experience if placed there. It does not indicate colour, line length, temperature, or the motion of the source charge. Therefore, option A is correct.

Correct answer: A. From positive to negative

Explanation: Electric field lines originate on positive charges and terminate on negative charges, so the field-line direction between unlike charges is from positive to negative. This agrees with the force direction on a positive test charge. Option B reverses the convention, option C describes neither a positive-negative pair, and option D is false. Thus option A is correct.

Correct answer: A. They bend away from each other

Explanation: Two equal positive charges repel one another, and the electric field is the vector sum of the fields produced by both charges. Between them, the field-line pattern therefore bends away from the region between the charges. Field lines do not intersect because the field cannot have two directions at one point, and electrostatic lines do not form closed circles. Hence A is correct.

Correct answer: A. By force on a test charge

Explanation: An electric field is identified through the force it produces on a charge. If a sufficiently small positive test charge is placed at a point and experiences a force, an electric field exists there; quantitatively, E = F/q for a test charge. Paper colour, air smell, and sound pitch are not defining effects of an electric field. Therefore option A is correct.

Correct answer: A. It decreases

Explanation: For a point charge, the electric-field magnitude is E = k|Q|/r². Thus, when the distance r increases, the field decreases according to the inverse-square law; doubling the distance makes the field one-fourth as large. Field lines also appear less dense farther away. Therefore option A is correct, while B and C contradict the formula.